Alloy of stainless steel and articles



United States Patent 3 082,083 ALLOY 0F STAINLEiSS STEEL AND ARTICLES Walter B. Levy, Palos Verdes Estates, Calif., and George N. Geller, Towson, Md., assignors to Armco Steel Corporation, a corporation of Ohio No Drawing. Filed Dec. 2, 1960, Ser. No. 73,196 7 Claims. (Cl. 75-428) Our invention relates to the alloy steels, more particularly the austenitic chromium-nickel stainless steels, and to Various articles of manufacture fashioned thereof.

One of the objects of our invention is the provision of an austenitic stainless steel which is strong and tough and yet which is free of magnetic effects under the conditions of actual use.

Another object is the provision of hotcold-worked products, for example forgings, of high strength and toughness but of very low magnetic permeability which low magnetic permeability is fully retained in use where cold-working as by hammering, pounding, sudden twisting, and the like, are encountered.

A further object of our invention is the production of a collar for oil drilling equipment (interconnecting the drill bit with the drill pipe), which collar is strong and tough and well calculated to Withstand the turning effect encountered in use as well as the hammering and pounding in coupling, uncoupling and moving the collar about an oil field without bending or taking a set, which collar is free of magnetic effects throughout the useful life of the same; and yet which is comparatively inexpensive in initial cost and in maintenance, and is well adapted to withstand the corrosive attacks of brine, hydrogen sulfide and the like encountered in an oil Well drilling operation.

Other objects of our invention in part will be obvious and in part pointed out during the course of the following description.

Accordingly, our invention resides in the combination of elements, composition of ingredients, and in the working steps, and in the relation between the same and the composition, as more particularly described herein and set out in the claims at the end of this specification.

Referring now more particularly to the practice of our invention, it may be noted at this point that the number of corrosion-resisting alloys now available to the art are legion. In the field of the stainless steels, alone, we venture to say that there are some sixty standard grades. These generally employ chromium in the amount of 10% to with or without nickel in amounts up to 30%, and remainder iron. Carbon is present, this usually in amounts less than .10% although in certain grades it is purposefully employed in amounts up to 1% or more. For special purposes there may be included in the composition of the steel significant amounts of any one or more of copper, molybdenum, cobalt, manganese and silicon, and small amounts of aluminum, titanium, vanadium and columbium. So, too, nitrogen may be employed for desired benefits. In some of the highly alloyed steels boron is found to be a beneficial addition.

Similarly, in the field of non-ferrous alloys there are a great variety of compositions known and used at the present time, the particular choice being dictated largely by the physical properties required, the availability and the cost. In many instances it is the required physical properties which point to the alloy to be used, even though the cost be high, and the availability somewhat uncertain because of the large amounts of critical elements employed. For example, in the construction of the drill collars employed in oil well drilling equipment it is not uncommon to resort to the expensive K-Monel (essentially 66% nickel, 30% copper and 3% aluminum), this because of the high strength requirements and the necessary freedom from magnetic effects under various conditions of use, all in spite of the high cost of the metal More particularly, the known drill collars range in size from an outside diameter of some 4 /2 to 8 inches, an inside diameter of about 2% to 2% inches, a length 01 some 14 -to 32 feet, and a weight of some 790 pound: to 3,400 pounds. Such a collar is employed to inter connect the drill bit with the drill pipe in an oil welj drilling string. And such a collar must admit the presence of an instrument (lowered through the pipe at ar appropriate position above the drill bit) which serves to measure the inclination of the hole being drilled anc' the direction of thisinclination. Such an instrument ir substantial part relies upon the magnetic effects of tilt earth. And, for accurate measurement, must be free or any magnetic effect coming from the drill bit, from the pipe or from the collar. The effects of bit and pipt are avoided by positioning the instrument well withir the length of the collar, and well away both from bi and pipe. Any effect of the collar is avoided by em ploying in its construction an alloy which under all con ditions of use and maintenance is entirely non-magnetic For this purpose there has been used the alloy known a: K-Monel. But this alloy is very expensive and require:

its composition to contain large quantities of nickel, t

metal which from time to time is viewed as highly stra tegic.

For drill collars there also have been used certaii alloy steels, particularly the highly alloyed chromium nickel steels. For example, the well known 188 chro mium-nickel steel has been employed for the purpose But with rough handling, as by hammering the drill col lar or pounding it in making or unmaking threaded en gagement with pipe and bit, or in slamming it arounr when not in use, it was feared that the metal would los its known non-magnetic characteristics and actually be come significantly magnetic. This would be sufficien to ruin the collar for further use with the sensitive in struments for drill-hole measurement.

Another alloy steel which for a time found favor is thi 15-l5 chromium-nickel stainless steel. And although thi retained its magnetic quality throughout use and non-us over long periods of time and under the conditions 0 abuse actually encountered in the field, this steel sufferer in other regards; it lacked the strength required to with stand the strains met with in prolonged periods of opera tion and occasionally was found to take a permanent set that is, it bent in use.

While many alloy steels of great strength and tough ness are known these fail to possess the combination 0 properties required in drill collars and similar articles 0 use. Accordingly, therefore, an object of our inventio: is the provision of an alloy steel which is strong, tougl corrosion-resistant, wear-resistant and free of magneti effects under the conditions encountered in actual prac tical use, which steel machines well in cutting, threadin and like operations and which is substantially less er mium and nitrogen, with the remainder of the compositio substantially all iron.

In our steel the amounts of th several ingredients and the relation between the same a1 .such that the steel is fully austenitic and completely fre of magnetic effects. The steel, in broad composition, analyzes carbon about .10% to .25%, manganese about 7% to 14%, nickel exceeding 6% but not exceeding 15%, with the sum of the manganese and nickel contents exceeding 14% but not exceeding 29%, chromium about 12% to 18%, nitrogen about .15% to 50%, and remainder substantially all iron. Small amounts of silicon, of course, are present, those usually not exceeding about 1.00%, however. Sulphur and phosphorus likewise commonly are present, these each usually not exceeding 0.050%, although where desired, there may be employed sulphur as a purposeful addition in amounts upto 0.15% to achieve improved machining characteristics.

The steel of our invention conveniently is melted, in accordance with any one of a number of practices well known in the art, in an electric arc furnace. Upon finishing the metal, the furnace is tapped. There are produced ingots of desired size and shape which are reheated and cogged down into forging billets for some applications or, for others, are reheated and rolled into slabs, blooms and billets for further conversion into plate, sheet, bars, wire, and the like. The metal works well in the hot mill. Moreover, it forges well. It also works well in various cold-rolling and cold-drawing operations. The steel is fully austenitic and non-magnetic in all conditions of hot-working, forging, cold-rolling and colddrawing.

We feel that the composition of our steel is highly critical in terms of the carbon, manganese, nickel, chromium, and nitrogen contents and the relation between these various ingredients. Consider first the carbon content of the metal. We feel that carbon definitely contributes to the yield strength of the steel; it is particularly beneficial in improving the yield strength through a hotcold-working or warm-working operation, as in forging the metal. At least .10% carbon is required; more than .25 however, can not be tolerated because the higher carbon contents results in a loss of ductility. Hot-workability suffers and so does the cold-workability.

The manganese content likewise is critical because we find that manganese contributes to an assured freedom from magnetic effects, that is, a low permeability. Desired results are had where the manganese content is as low as 7% and as high as 14%. With manganese less than 7% the fully non-magnetic quality of the steel is lost with severe cold-working and with more than 14% manganese the mechanical properties are inclined to suffer, so also the corrosion-resistance to certain media.

As to the nickel content, we find that this must exceed 6% in order to assure a stably austenitic structure under all conditions of heat-treatment and under all conditions of working; that is, hot-working into blooms, billets, bars, plate, and the like; cold-working into sheet, strip, bars, rods and wire at the mill and into various products at the plant of a customer-fabricator as by bending, pressing, stamping, punching, cutting, drilling, machining and threading; warm-working as in forging into desired special shapes by hot-forging or warm-forging; and even cold-working in ultimate use as byhammering, pounding, twisting or bending. A nickel content in excess of 15% is not desirable because it increases the cost of the steel and, of even greater importance, it results in a loss of mechanical properties.

In order that a fully austenitic structure be had which is free of magnetic effects in the work-hardened condition, particularly under the various conditions encountered in actual use, for example a drill collar, certain of which are indicated above, it is necessary that the sum of manganese and nickel contents of our steel be in excess of 14%. The sum of these two ingredients should be maintained at a value exceeding 14% for the further reason that with less than that amount there is an inclination toward the formation of delta-ferrite with a consequent loss in hot-working properties; the metal is likely some l800 to 2100 F.

to split in hot-working. It is not desired, however, that the sum of the ingredients exceed 29% because, as noted abpve in connection with the individual contents of manganese and nickel, the excess results in an undesired loss of mechanical properties.

The chromium content of our steel is important and critical because with a chromium content less than 12% the corrosion-resistance suffers. With chromium exceeding 18% it becomes difiicult to maintain the structural balance necessary to assure a fully austenitic condition under all conditions, there is an inclination to develop delta-ferrite which is harmful to the magnetic properties and also adversely affects the hot-workability.

And, finally, the nitrogen content is considered to be critical; it contributes to the austenitic structure and to the yield strength of the metal as well. Where the nitrogen content is less than .15 no significant effect is felt and where it is greater than .50% there is chance of gassiness with the possibility of ruining the steel for useful applications. Moreover, an excessive nitrogen content increases hot-working difficulties, also warm-forging difiiculties.

None of the ingredients sulphur, phosphorus or silicon is essential to our steel; these customarily are present, however, as impurities as noted above. Sulphur is ad vantageously added where considerable machining is to be expected in making the product of ultimate use. But the sulphur content, however, should not exceed .15 for with a higher sulphur content the steel becomes unsuited to applications where hot-cold work must be resorted to, as for example, in warm-forging operations. Actually, in a steel intended for forging, we prefer to maintain the sulphur content, like the phosphorus content, at a maximum of .050%, and preferably a maximum of .030%.

While, as noted above, the steel of our invention broadly analyzes: carbon .10% to .25%, manganese 7% to 14%, nickel exceeding 6% but not exceeding 15%, with the sum of the manganese and nickel contents in excess of 14% but not exceeding 29%, chromium 12% to 18%, nitrogen .15% to 50%, and remainder substantially ail iron, we prefer a steel analyzing: carbon .13% to .17%, manganese 9% to 11%, nickel 7% to 9%, chromium 14% to 16%, nitrogen 25% to 35%, and remainder substantially all iron. This steel is particularly suited to drastic cold-working and cold-forming operations in fabrication by a customer-fabricator all while retaining a fully austenitic structure, a structure free of magnetic effects, i.e., a permeability not exceeding about 1.007.

One specific preferred steel of our invention analyzes carbon about .15 manganese about 10%, nickel about 8%, chromium about 15%, nitrogen about 30%, and remainder substantially all iron.

In working one of our preferred specific steels into a drill collar in accordance with the teachings of our invention, we rough forge a steel billet analyzing carbon .13% to .17%, manganese 9% to 11%, nickel 7% to 9%, chromium 14% to 16%, nitrogen 25% to 35%, 30% to .70% silicon, 030% max. sulphur, .030% max. phosphorus, and remainder iron, at a temperature of The steel is then reheated and further forged, this at a temperature of about 1300 to 1500 F. The amount of reduction achieved with the forging at 1300 to 1500 F. is on the order of 20%, the limiting factor, of course, being the resistance of the work to deformation reaching the capacity of the press. But even with the forging and the drastic hot-cold or warm-working that the metal receives it is noted that the steel retains its fully austenitic structure and the permeability is not increased above about 1.007.

The mechanical properties of the specific steel noted immediately above, in both conditions of forging, that is, forged at 1800 to 2100 F. and further forged at 1300 to 1500 F. for a further reduction of about 20%, are given in Table I below:

TABLE I Mechanical Properties of Carbon-Manganese-Nickel- Chromium-Nitrogen Steel Forgings The forged steel is seen to be strong and tough. It lends itself to a variety of machining operations such as boring, threading, cutting, and the like. It readily may be welded where desired. And with it all the metal retains its non-magnetic quality.

While a forged and machined drill collar pursuant to our teachings preferably analyzes carbon .13% to .17%, manganese 9% to 11%, nickel 7% to 9%, chromium 14% to 16%, nitrogen 25% to .35%, and remainder substantially all iron, it, of course, will be understood that the forged drill collar, or indeed other forgings, advantageously may be fashioned of steel of somewhat broader analysis, for example carbon .lO% to .25 manganese 7% to 14%, nickel exceeding 6% but not exceeding 15%, with the sum of the manganese and nickel contents exceeding 14% but not exceeding 29%, chromium 12% to 18%, nitrogen, .15% to .50%, and remainder subs-tantially all iron. The forgings are fully austenitic, with magnetic permeability not exceeding 1.007. Moreover, they are of good strength and toughness, the ultimate strength amounting to at least 100,000 p.s.i.

Thus it will be seen that we provide in our invention a carbon manganese nickel chromium nitrogen steel in which the various objects hereinbefore set forth are successfully achieved. The steel is fully austenitic and free of delta-ferrite at hot-working temperatures, it readily lends itself to hot-working, for example hot-rolling, and also lends itself to a variety of cold-working operations such as cold-drawing and cold-rolling, and warm-Working or hot-cold-working such as forging. The steel does not develop a magnetic phase as a result of the cold-working or Warm-working operations but, rather, it remains fully austenitic and non-magnetic. Various articles fashioned thereof, therefore, are eminently suited to applications where a combination of strength, corrosion-resistance and freedom from non-magnetic effects are required for example in the drill collar of an oil well drilling string. In such an application a sensitive magnetic measuring instrument is supported within the collar (and well above the drill bit and below the drill pipe) for precise measurement of the deviation and direction of the drill hole. Another application is a non-magnetic window frame for high energy particle acceleration machines.

Since many embodiments may be made of our invention, and since numerous variations may be made in the embodiments described herein, it will be understood that all matter described herein is to be interpreted as illustrative and not as a limitation.

We claim as our invention:

1. An alloy steel, which when cold-Worked or warm- Worked to the extent of about 20% reduction in area has good yield strength in combination with a magnetic permeability not exceeding about 1.007, said steel essentially consisting of carbon .10% to 25%, manganese 7% to 14%, nickel exceeding 6% but not exceeding 15%, with the sum of the manganese and nickel contents exceeding 14% but not exceeding 29%, chromium 12% to 18%, nitrogen .15% to 50%, and remainder essentially iron.

2. An alloy steel, which when cold-Worked or warmworked to the extent of about 20% reduction in area has good yield strength in combination with a magnetic permeability not exceeding about 1.007, said steel essentially consisting of carbon .13% to .17%, manganese 9% to 11%, nickel 7% to 9%, chromium 14% to 16%, nitrogen 25% to .35 and remainder essentially iron.

3. An alloy steel, which when cold-worked or warmworked to the extent of about 20% reduction in area has good yield strength in combination with a magnetic permeability not exceeding about 1.007, said steel essentially consisting of carbon .13% to .17%, manganese 9% to 11%, nickel 7% to 9%, chromium 14% to 16%, nitrogen .25 to .35 up to .15 sulphur, and remainder essentially iron.

4. A non-magnetic alloy steel forging which at a reduction in area of some 20% has a magnetic permeability not exceeding about 1.007, a yield strength of at least about 60,000 p.s.i., and an ultimate tensile strength 01 at least about 100,000 p.s.i., said steel forging consisting essentially of carbon .10% to .25%, manganese 7% tc 14%, nickel exceeding 6% but not exceeding 15 with the sum of the manganese and nickel contents exceeding 14% but not exceeding 29%, chromium 12% to 18%, nitrogen .15 to 50%, and remainder essentially iron.

5. A non-magnetic alloy steel forging which at a reduction in area of some 20% has a magnetic permeability not exceeding about 1.007, a yield strength of at least about 100,000 p.s.i., said forging consisting essentially 01 carbon .13% to .17%, manganese 9% to 11%, nickel 7% to 9%, chromium 14% to 16%, silicon 30% to .70% nitrogen .25% to .35 and remainder essentially iron.

6. A hot-cold-worked alloy steel drill collar with magnetic permeability not exceeding about 1.007 for a reduction in area of some 20%, said collar essentially consisting of carbon .lO% to .25 manganese 7% to 14%, nickel 6% to 15% chromium 12% to 18%, nitrogen .15% tc .50%, and remainder essentially iron.

7. A forged alloy steel drill collar with magnetic permeability not exceeding about 1.007 for a reduction i1: area of some 20%, said collar essentially consisting 01 carbon .13% to .17%, manganese 9% to 11%, nickel 7% to 9%, chromium 14% to 16%, nitrogen 25% tc .35 and remainder essentially iron.

References Cited in the file of this patent UNITED STATES PATENTS 2,876,096 Payson Mar. 3, 1952 2,890,955 Stanley et a1 June 16, 1955 2,891,858 Kegerise et al June 23, 1955 2,894,833 'Linnert et al July 14, 1959 2,903,386 Waxweiler Sept. 8, 1955 2,955,034 Korchynsky et al. Oct. 4, 196( 

1. AN ALLOY STEEL, WHICH WHEN COLD-WORKED OR WARMWORKED TO THE EXTENT OF ABOUT 20% REDUCTION IN AREA HAS GOOD YIELD STRENGTH IN COMBINATION WITH A MAGNETIC PERMEABILITY NOT EXCEEDING ABOUT 1.0007, SAID STEEL ESSENTIALLY CONSISTING OF CARBON .10% TO .25%, MANGANESE 7% TO 14%, NICKEL EXCEEDING 6% BUT NOT EXCEEDING 15%, WITH THE SUM OF THE MANAGANESE AND NICKEL CONTENTS EXCEEDING 14% BUT NOT EXCEEDING 29%, CHROMIUM 12% TO 18%, NITROGEN .15% TO .50%, AND REMAINDER ESSENTIALLY IRON. 